1. Field of the Invention
The present invention relates to a slave light-emission controlling device that controls, in response to a light emitted by a master flash device, a salve light emission of an auxiliary light-emitting part.
The present invention also relates to a slave flash device having a slave light-emission controlling device built therein.
2. Description of the Related Art
An increased flash photographing method is known, in which when a flash illumination is provided in synchronization with taking a picture by a camera and amount of light of a single flash device (master flash device) is insufficient for the flash illumination, an auxiliary light-emitting part is also used to emit an additional light to compensate for the insufficiency of the amount of light.
Also known is a multiple flash photographing method in which a subject to be imaged is illuminated from a plurality of directions so as to control the shading balance of the subject.
However, many of compact digital cameras developed in recent years are equipped with no means for electrically connecting with external flash devices.
Then, in order to implement such a photographing method as described above, there have been developed a slave flash device that detects, using a sensor, a light emission of a flash device built in the camera and provides a slave light emission, and a slave light-emission controlling device (that is to be attached to a flash device for controlling a slave light emission, also called as a slave unit).
For example, Japanese Examined Patent Application Publication No. Sho 58-21798 proposes, as an increased-flash illumination approach, a method for controlling a slave flash device in such a manner that operation of the slave flash device is wirelessly associated with start and stop of a light emission of another flash device.
In the meantime, many digital cameras with built-in flash devices provide a small amount of pre-flash light emission just before making an exposure. Such a digital camera uses an imaging sensor to photometer a light reflected from a subject, calculates an appropriate amount of a main flash from the photometered amount of reflected light, and decides a flash time of the main flash. Then, the digital camera controls the flash time of the main flash based on the decided time. This method is simple and widely used because the image sensor can be utilized as a dimmer sensor. Some cameras provide a plurality of pre-flashes just before making an exposure.
However, the conventional slave flash devices and slave units consume a large part of a stored energy in response to a pre-flash of the built-in flash devices. Because of this, the remaining part of the stored energy will be insufficient at the time of an actual main flash, and thus the slave light emission cannot be used for the increased-flash illumination.
In order to solve the above problem, Japanese Unexamined Patent Application Publication No. 2000-29102 proposes a slave flash device that is not responsive to a pre-flash of the built-in flash device but only responsive to a main flash thereof to provide a slave light emission.
The method of Japanese Unexamined Patent Application Publication No. 2000-29102 described above has a problem that the slave flash device always provides a full light emission (i.e., a light emission consuming the entire energy stored) and hence cannot appropriately control the amount of light emission.
And so, an object of the present invention is to provide a slave light-emission controlling device and a slave flash device for performing a light emission in association with a pre-flash of a master flash device and obtaining a correct exposure.
The present invention will now be described below.
(1) A slave light-emission controlling device of the present invention controls, in response to a light emission of a master flash device, a slave light emission of an auxiliary light-emitting part. This slave light-emission controlling device includes a light receiving part and a flash light amount ratio controlling part.
The light receiving part receives light of the master flash device.
The flash light amount ratio controlling part controls a pre-flash light amount ratio and a main flash light amount ratio based on pre-flash and main flash lights of the master flash device received by the light receiving part so that these flash light amount ratios are caused to be approximately equal to each other, said pre-flash light amount ratio being a ratio in amount of light between the pre-flash light of the master flash device and a pre-flash light of the auxiliary light-emitting part, and said main flash light amount ratio being a ratio in amount of light between the main flash light of the master flash device and a main flash light of the auxiliary light-emitting part.
(2) Preferably, the flash light amount ratio controlling part causes stop of a light emission of the auxiliary light-emitting part to delay relative to stop of a light emission of the master flash device by a time that is approximately equal to the time by which start of the light emission of the auxiliary light-emitting part delays relative to start of the light emission of the master flash device.
(3) Preferably, the flash light amount ratio controlling part controls timing of the stop of light emission of the auxiliary light-emitting part during pre-flash, thereby adjusting total amount of flash light during the pre-flash.
(4) Preferably, the flash light amount ratio controlling part changes a discharging time of a light emission detection charge by using a charge storage part included in the light receiving part and/or a charge storage part connected in parallel with the light receiving part, and causes the pre-flash and main flash light amount ratios to be approximately equal to each other, the light emission detection charge being outputted from the light receiving part when a light emitted by the master flash device is received by the light receiving part.
(5) Another slave light-emission controlling device of the present invention controls a slave light emission of an auxiliary light-emitting part in response to a light emission of a master flash device. This slave light-emission controlling device includes a light receiving part and a flash-time ratio controlling part.
The light receiving part detects start and stop of a light emission of the master flash device.
The flash-time ratio controlling part controls a pre-flash time ratio and a main flash time ratio so that these flash time ratios are caused to be approximately equal to each other, said pre-flash time ratio being a time ratio between a pre-flash time of the master flash device and a pre-flash time of the auxiliary light-emitting part, and said main flash time ratio being a time ratio between a main flash time of the master flash device and a main flash time of the auxiliary light-emitting part.
(6) A slave flash device of the present invention includes a slave light-emission controlling device as described in the foregoing (1) and an auxiliary light-emitting part whose light emission is controlled by the slave light-emission controlling device.
(7) Another slave flash device of the present invention includes a slave light-emission controlling device as described in the foregoing (5) and an auxiliary light-emitting part whose light emission is controlled by the slave light-emission controlling device.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by identical reference numbers, in which:
FIG. 1 is a diagram showing a slave circuit of a slave flash device;
FIG. 2 is a diagram showing signal waveforms developed at the corresponding positions in the slave circuit;
FIG. 3 is a diagram showing the state of a light emission during a flash assisted image pickup of a digital camera;
FIG. 4 is a diagram showing the state in which the slave flash device is cooperating with the digital camera; and
FIG. 5 is a diagram showing the light emission waveform of a built-in flash device and that of the slave flash device.